Engineering topics

Smadja, G.

Publications and source records attributed to Smadja, G..

5 records

DOE OSTI2024

Intrinsic and extinction colour components in SNe Ia and the determination of R V

Context.The colour fluctuations of type Ia supernovae (SNe Ia) include intrinsic and extrinsic components, which both contribute to the observed variability. Previous works proposed a statistical separation of these two contributions, but the individual intrinsic colour contributions of each SN Ia were not extracted. In addition, a large uncertainty remains on the value of the parameterR V , which characterises the dust extinction formula. Aims.Leveraging the known parameterisation of the extinction formula for dust in our Galaxy, and applying it to the host galaxy of SNe Ia, we propose a new method of separation –valid for each SN– using the correlations between colour fluctuations. This also allows us to derive a well-constrained value of the extinction parameterR V with different, possibly smaller systematic errors. We also define a three-dimensional space of intrinsic colour fluctuations. Methods.The key ingredients in this attempt at separating the intrinsic and extinction colour components for each SN –and subsequently measuringR V – are the assumption of a linearized dependence of magnitude on the extinction component of colour, a one-dimensional extra-intrinsic colour space (in addition to CaII H&Kλ3945 and Si IIλ4131 contributions) over four independent colours, and the absence of correlation between the intrinsic and extrinsic variabilities. Results.We show that a consistent solution is found under the previous assumptions, but the observed systematic trends point to a (small) inadequacy of the extinction formula. Once corrected, all systematic extinction effects can be cancelled by choosing a single scaling of the extinction colour component as well as an appropriate value ofR V = 2.181 ± 0.117. The observed colours are described within an accuracy of 0.025 mag. The resulting magnitude variability is 0.13 over allUBVRIbandpasses, and this fluctuation is shown to be independent of the bandpass to within 0.02 mag.

Astronomy & Astrophysics↗

DOE OSTI2022

A Probabilistic Autoencoder for Type Ia Supernova Spectral Time Series

We construct a physically parameterized probabilistic autoencoder (PAE) to learn the intrinsic diversity of Type Ia supernovae (SNe Ia) from a sparse set of spectral time series. The PAE is a two-stage generative model, composed of an autoencoder that is interpreted probabilistically after training using a normalizing flow. We demonstrate that the PAE learns a low-dimensional latent space that captures the nonlinear range of features that exists within the population and can accurately model the spectral evolution of SNe Ia across the full range of wavelength and observation times directly from the data. By introducing a correlation penalty term and multistage training setup alongside our physically parameterized network, we show that intrinsic and extrinsic modes of variability can be separated during training, removing the need for the additional models to perform magnitude standardization. We then use our PAE in a number of downstream tasks on SNe Ia for increasingly precise cosmological analyses, including the automatic detection of SN outliers, the generation of samples consistent with the data distribution, and solving the inverse problem in the presence of noisy and incomplete data to constrain cosmological distance measurements. We find that the optimal number of intrinsic model parameters appears to be three, in line with previous studies, and show that we can standardize our test sample of SNe Ia with an rms of 0.091 ± 0.010 mag, which corresponds to 0.074 ± 0.010 mag if peculiar velocity contributions are removed.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2020

Strong dependence of Type Ia supernova standardization on the local specific star formation rate

As part of an on-going effort to identify, understand and correct for astrophysics biases in the standardization of Type Ia supernovae (SN Ia) for cosmology, we have statistically classified a large sample of nearby SNe Ia into those that are located in predominantly younger or older environments. This classification is based on the specific star formation rate measured within a projected distance of 1 kpc from each SN location (LsSFR). This is an important refinement compared to using the local star formation rate directly, as it provides a normalization for relative numbers of available SN progenitors and is more robust against extinction by dust. We find that the SNe Ia in predominantly younger environments are Δ Y = 0.163 ± 0.029 mag (5.7 σ ) fainter than those in predominantly older environments after conventional light-curve standardization. This is the strongest standardized SN Ia brightness systematic connected to the host-galaxy environment measured to date. The well-established step in standardized brightnesses between SNe Ia in hosts with lower or higher total stellar masses is smaller, at Δ M = 0.119 ± 0.032 mag (4.5 σ ), for the same set of SNe Ia. When fit simultaneously, the environment-age offset remains very significant, with Δ Y = 0.129 ± 0.032 mag (4.0 σ ), while the global stellar mass step is reduced to Δ M = 0.064 ± 0.029 mag (2.2 σ ). Thus, approximately 70% of the variance from the stellar mass step is due to an underlying dependence on environment-based progenitor age. Also, we verify that using the local star formation rate alone is not as powerful as LsSFR at sorting SNe Ia into brighter and fainter subsets. Standardization that only uses the SNe Ia in younger environments reduces the total dispersion from 0.142 ± 0.008 mag to 0.120 ± 0.010 mag. Overall, we show that as environment-ages evolve with redshift, a strong bias, especially on the measurement of the derivative of the dark energy equation of state, can develop. Fortunately, data that measure and correct for this effect using our local specific star formation rate indicator, are likely to be available for many next-generation SN Ia cosmology experiments.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS1972

A liquid xenon radioisotope camera.

A new type of gamma-ray camera is discussed that makes use of electron avalanches in liquid xenon and is currently under development. It is shown that such a radioisotope camera promises many advantages over any other existing gamma-ray cameras. Spatial resolution better than 1 mm and counting rates higher than one million C/sec are possible. An energy resolution of 11% FWHM has recently been achieved with a collimated Hg-203 source using a parallel-plate ionization chamber containing a Frisch grid.

Zaklad, H.↗

NASA NTRS1971

Liquid-filled proportional counter

Liquid Xe filled single wire proportional and multiple wire ionization chambers, measuring gain and time/spatial resolution properties

Alvarez, L. W.↗